Again, this liturgical myth is a past practice, but not a rule. In fact, the tabernacle does not need to be in the sanctuary of the church at all.
This is because the tabernacle’s purpose is not liturgical. Tabernacles were introduced for the reservation of communion for taking to the sick and housebound. Eucharistic devotions also developed as a result. In the Mass, however, the eucharistic focal point is the altar, upon which the memorial sacrifice of the Mass is offered.
The General Instruction of the Roman Missal (no. 315) gives directions as to where the tabernacle can be located:
Consequently, it is preferable that the tabernacle be located, according to the judgment of the diocesan Bishop:
a. Either in the sanctuary, apart from the altar of celebration, in a form and place more appropriate, not excluding on an old altar no longer used for celebration;
b. Or, likewise, in some chapel suitable for the faithful’s private adoration and prayer and organically connected to the church and readily visible to the Christian faithful.
A separate chapel can give the tabernacle the dignity it would also receive the sanctuary, but make the important distinction between it and the altar; a distinction blurred somewhat by the arrangement of churches prior to the Second Vatican Council when the tabernacle sat on the altar. In some churches, it is not possible to create a suitable chapel without significant remodelling, and a sanctuary position is therefore required.
So there are two possible locations for the tabernacle. In cathedrals, it is a long-held tradition and law that the tabernacle must be located in a separate chapel, as we see in our cathedral in Parramatta. Finally, the Holy Thursday liturgy requires reposition of the eucharist in a tabernacle located outside the main body of the Church. A tabernacle in a separate chapel is such a place.
the link above to St. Patrick’s Cathedral, Parramatta is a photograph of the Inauguration of the Blessed Sacrament Chapel at the Cathedral’s dedication, 29 November 2003. Other photos are accessible via the St. Patrick’s Cathedral page of the Diocese of Parramatta website